Lasers are commonly used as the source of light signals in optical communications systems. These lasers are often integrated onto optical chips and/or onto optoelectronic chips. The laser cavities in these lasers can be external cavity lasers configured to output a light signal with a single wavelength or a single longitudinal cavity mode. One of the challenges with these lasers is mode hopping. Mode hopping refers to shift in output light wavelength when laser switches from one longitudinal mode to another. The change between modes is associated with an undesirable discrete change in the wavelength (and sometimes power) of the light signal output by the laser. These changes are a source of bit error in optical links.
The mode hopping can be a result of influences that change the index of refraction of the media through which the light signals are guided in the laser cavity. Examples of influences that can cause these effects are temperature changes, changes in the level of electrical current applied to the laser cavity, or aging of the gain medium. In order to address these problems, many of these devices include components for stabilizing the indices of refraction of the media through which the light signals are guided. These components increase the complexity, cost, and power consumption of the device.